The present invention relates to a presensitized plate for use in making a lithographic printing plate (hereinafter referred to as "PS plate" and more specifically to a PS plate comprising a specific o-naphthoquinonediazide compound.
There have been widely used aluminum plates as substrates for lithographic printing plates. These aluminum plates are surface-treated for improving the hydrophilicity and water-retention characteristics of the plates, for improving the adhesion thereof to image areas and for improving the strength of non-image areas of the resulting PS plates. These aluminum plates have been surface-treated by, for instance, mechanical surface-roughening treatments such as ball graining, wire graining and brush graining; electrolytic surface-roughening treatments by passing a DC or AC current through the aluminum plates in a hydrochloric acid or nitric acid bath; or any combination thereof. After the surface-treatment, these aluminum plates are anodized in a sulfuric acid or phosphoric acid bath.
The aluminum plate may optionally be subjected to sealing treatment with a silicate or hot water and/or to a dipping treatment in, for instance, a polyvinylsulfonic acid solution. It has been well-known that a PS plate is prepared by applying, onto the aluminum substrate thus prepared, a light-sensitive composition comprising an o-naphthoquinonediazide as a light-sensitive compound and a binder such as a novolak resin, vinyl resin or urethane resin.
In addition, it has already been known that the use of a reaction product of a polyhydroxy compound with an o-naphthoquinonediazide compound such as an o-naphthoquinonediazide light-sensitive compound permits, for instance, the inhibition of crystal-deposition in the resulting light-sensitive layer and the improvement of storability, adhesion to an aluminum substrate, and the chemical resistance and developability of the light-sensitive layer.
Examples of light-sensitive compositions containing such reaction products include those comprising o-naphthoquinonediazidesulfonic acid esters of polycondensed resins of pyrogallol and acetone as disclosed in Japanese Patent Publication for Opposition Purpose (hereinafter referred to as "J. P. KOKOKU") No. Sho 43-28403 (=U.S. Pat. No. 3,635,704); those comprising o-naphthoquinonediazidesulfonic acid esters of polycondensed resins of pyrogallol/resorcin mixture with acetone for controlling the developability of the resulting light-sensitive layer as disclosed in Japanese Un-examined Patent Publication (hereinafter referred to as "J. P. KOKAI") No. Sho 55-76346; and those comprising polycondensed resins of polyhydric phenols with benzaldehyde or acetaldehyde for improving the developability and chemical resistance of the resulting light-sensitive layer as disclosed in J. P. KOKAI Nos. Sho 50-1044 and Sho 50-1045.
However, the following problems have become evident after conducting various studies using these o-naphthoquinonediazidesulfonic acid esters of these polycondensed resins of polyhydroxy phenols with ketones or aldehydes.
A positive-working lithographic printing plate is, in general, prepared by pasting a plurality of original films carrying various pictures, patterns and/or characters on a transparent base to form a positive film, putting the film on the light-sensitive layer of a PS plate, exposing the assembly to ultraviolet rays and then developing the exposed PS plate with a developer. If the resulting lithographic printing plate requires highly improved printing durability, the plate is then subjected to a burning treatment to thermally harden the light-sensitive layer on the image area thereof. When the foregoing positive film is put on a light-sensitive layer comprising a conventional o-naphthoquinonediazidesulfonic acid ester of a polycondensed resin of a polyhydroxy phenol with a ketone or an aldehyde and then the assembly is exposed to light, however, the light-sensitive layer behind the edge portion of various original films pasted on the base film of the positive film used remains on the plate in a semi-exposed state. The semi-exposed light-sensitive layer is strongly adhered to the plate surface, cannot easily be removed with a developer and thus remains unremoved even after the completion of the development. The use of the resulting printing plate in printing operations results in background contamination of copies. The pasting marks thus formed on the exposed PS plate cannot completely be removed with a so-called non-toxic erasing solution (free of hydrofluoric acid as a violet poison) generally used for the treatment of positive-working PS plates. The pasting marks become more conspicuous when the plate is subjected to a burning treatment commonly used for improving the printing durability of the resulting lithographic printing plate and accordingly, the resulting printing plate cannot be used in printing operations.
Nevertheless, the light-sensitive layer comprising a conventional o-naphthoquinonediazidesulfonic acid ester of a polycondensed resin of a polyhydroxy phenol with a ketone or an aldehyde never suffers from such a trouble that the layer on the image portion is dissolved out in a developer having a high concentration, unlike those comprising other known o-naphthoquinonediazidesulfonic acid esters of 2,3,4,4'-tetrahydroxybenzophenone or phenols such as m-cresol). More specifically, the light-sensitive layer exhibits an advantage in that it has a wide development latitude.